Thank you, DSatz! That's very helpful. I appreciate the detailed answer on their design and it will probably convince me to purchase and make the KK 18x > LC 4 active rig setup I've been thinking about for over a year now.
I agree that the KM 100 design, while perhaps not as efficient as the existing patented design, was both elegant and honorable. The AK series have always been wonderful microphones and this design constraint was trivial in terms of performance. I can only imagine the manufacturing challenges it created, having to assemble the delicate FET circuit on the back side of every capsule. Any mistake would be quite costly! To say that the AK capsule is a marvel of modern engineering might be an understatement.
Unfortunately, this design constraint did make AK capsules
considerably more expensive than other interchangeable capsule systems. Every time you wanted to add another pattern to your recording rig you had to pay a huge premium on each capsule. While this might not have been a concern for Neumann's primary consumer base, concert tapers almost always own more capsules that bodies and as a result I know very few tapers that have owned multiple Neumann AK patterns.
When I look at the KK A (and KK D) series, it's obvious how much better they are in every way. It's a smaller physical design, which is important to many tapers, and every component is more affordable than (or on par with) the KM 100 series. I believe every KK capsule is at least 25% cheaper than its AK equivalent (when they were still offered) and the price of bodies or the LC active cable did not really go up at all. It's a win-win all around.
That said, the series has been out for several years now and there has been practically no adoption in our community. The KM 100 series is still the microphone most people know about and use and I only personally aware of one recordist here that owns a KM A rig. Maybe there's a few more, but it's not a lot.
Considering that active cable setups are all the rage, I think the KK A series has to be an ideal candidate. Two KK capsules, a pair of LC 4 cables, and Naiant PFAs terminations would make for an incredible setup at a ridiculously good price. There's not a lot of tapers that want to use bodies these days, but for those that do the KK A is of course available and competitively priced with just about any other manufacturer. I guess I will have to be the pioneer here.